[1] Univ Maryland, Dept Physiol, Sch Med, Baltimore, MD 21201 USA
[2] Univ Maryland, Ctr Med Biotechnol, Inst Biotechnol, Baltimore, MD 21201 USA
[3] Univ Calif Berkeley, Dept Mol & Cell Biol, Berkeley, CA 94720 USA
[4] Univ Calif San Francisco, Dept Biochem, San Francisco, CA 94143 USA
[5] UCL, Dept Physiol, London WC1E 6BT, England
[6] Princeton Univ, Dept Mol Biol, Princeton, NJ 08544 USA
[7] Princeton Univ, Program Neurosci, Princeton, NJ 08544 USA